I. Field of the Invention
The present invention relates to an impulse ink jet print head comprised of a plurality of arrays mounted in an inclined and stacked manner for compactness and for accommodating variations in nozzle to paper distance. The present invention also relates to a new method of using an impulse ink jet print head.
II. Description of the Prior Art
Ink jet system, and particularly impule ink jet systems, are well known in the art. The principle behind an impulse ink jet as embodied in the present invention is the displacement of ink and the subsequent emission of ink droplets from an ink chamber through a nozzle by means of a driver mechanism which consists of a transducer (e.g., of piezoceramic material) bonded to a thin diaphragm. When a voltage is applied to the transducer, the transducer attempts to change its planar dimensions, but because it is securely and rigidly attached to the diaphragm, bending occurs.
This bending displaces ink in the chamber, causing outward flow both through an inlet from the ink supply, or restrictor, and through an outlet or nozzle. The relative fluid impedances of the restrictor and nozzle are such that the primary outflow is through the nozzle. Refill of the ink chamber after a droplet emerges from the nozzle results from the capillary action of the ink meniscus within the nozzle which can be augmented by reverse bending of the transducer. Time for refill depends on the viscosity and surface tension of the ink as well as the impedance of the fluid channels. A subsequent ejection will then occur but only when refill has been accomplished and when, concurrently, the amplitude of the oscillations resulting from the first ejection have become negligible. Important measures of performance of an ink jet are the response of the meniscus to the applied voltage and the recovery time required between droplet ejections having uniform velocity and droplet diameter.
In general, it is desirable to employ a geometry that permits several nozzles to be positioned in a densely packed array. In such an array, however, it is important that the individual nozzles eject ink droplets of uniform diameter and velocity even at varying droplet ejection rates.
Some representative examples of the prior art will now be described. U.S. Pat. No. 3,107,630 to Johnson et al is an early disclosure of the use of piezoceramic transducers being utilized to produce a high frequency cyclic pumping action. This was followed by U.S. Pat. No. 3,211,088 to Naiman which discloses the concept of an impulse ink jet print head. According to Niaman, when a voltage is applied to a transducer, ink is forced through the nozzle to form a spot upon a printing surface. The density of the spots so formed is determined by the number of nozzles employed in a matrix. Another variation of print head is disclosed in U.S. Pat. No. 3,767,120 issued to Stemme which utilizes a pair of chambers positioned in series between the transducer and the discharge nozzle.
Significant improvements over then then existing prior art are disclosed in a series of patents issued to Kyser et al, manely, U.S. Pat. Nos. 3,946,398, 4,189,734, 4,216,483, and 4,339,763. According to each of these disclosures, fluid droplets are projected from a plurality of nozzles at both a rate and in a volume controlled by electrical signals. In each instance, the nozzle requires that an associated transducer, and all of the components, lie in planes parallel to the plane of the droplets being ejected.
A more recent disclosure of an ink jet print head is provided in the U.S. Pat. No. 4,525,728 issued to Koto. In this instance, the print head includes a substrate having a plurality of pressurization chambers of rectangular configuration disposed thereon. Ink supply passages and nozzles are provided for each pressurization chamber. Each chamber also has a vibrating plate and a piezoceramic element which cooperate to change the volume of the pressurization chamber to cause ink to be ejected from the respective nozzles thereof.
In many instances of the prior art, ink jet print heads are assembled from a relatively large number of discrete components. However, the cost of such a construction is generally very high. For example, an array of ink jets requires an array of transducers.
Typically, each transducer is separately mounted adjacent to the ink chamber of each jet by an adhesive bonding technique. This presents a problem when the number of transducers in the array is greater than, for example, a dozen, because complications generally arise due to increased handling complexities, for example, breakage or failure of electrical connections. In addition, the time and parts expense rise almost linearly with the number of separate transducers that must be bonded to the diaphragm. Furthermore, the chances of a failure or a wider spread in performance variables such as droplet volume and speed, generally increase. Additionally, in many instances, prior art print heads were large and cumbersome and could accommodate relatively few nozzles within the allotted space.
Typical ink jet arrays for print heads are fabricated by stacking thin laminations of steel or glass with appropriate openings and passages. Component parts are: the diaphragm which supports the piezoceramic transducers or drivers, the ink chamber, the nozzle plate, the inlet restrictor, the ink supply manifold and the base plate. In order to achieve close nozzle spacing and yet provide sufficient size for the transducers, various methods of fanning, interlacing and long passges between transducer and nozzle are used. In some arrangements the nozzles are located in the center of a planar surface. Others run the ink passsages to the edge of the laminate stack and either have a rectangular orifice made of a multiple of laminates or form a normal round orifice by placing an additional plate at right angles to the laminations. However, in most instances these prior constructions did not achieve the compactness and level of quality required for commercial applications.